Multiplicity of the β Form of the cAMP-dependent Protein Kinase Inhibitor Protein Generated by Post-translational Modification and Alternate Translational Initiation

• Published in: The Journal of biological chemistry Vol. 272; no. 32; pp. 20011 - 20020
• Main Authors: Kumar, Priyadarsini, Van Patten, Scott M., Walsh, Donal A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 08-08-1997
• Subjects: Amino Acid Sequence; Animals; Brain Chemistry; Carrier Proteins - chemistry; Carrier Proteins - metabolism; Carrier Proteins - pharmacology; Cyclic AMP-Dependent Protein Kinases - antagonists & inhibitors; Cyclic AMP-Dependent Protein Kinases - metabolism; Cyclic GMP-Dependent Protein Kinases - antagonists & inhibitors; Cyclic GMP-Dependent Protein Kinases - metabolism; Electrophoresis, Gel, Two-Dimensional; Enzyme Inhibitors - metabolism; Enzyme Inhibitors - pharmacology; Intracellular Signaling Peptides and Proteins; Male; Molecular Sequence Data; Molecular Weight; Phosphorylation; Protein Biosynthesis; Protein Processing, Post-Translational; Rats; Terminology as Topic; Testis - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.32.20011

Two distinct species of the thermostable inhibitor of the cAMP-dependent protein kinase, PKIα and PKIβ, exist that are the products of separate genes. The PKIβ form, as first isolated from rat testis, is a 70-amino acid protein, but the genomic sequence suggested that an alternate form might exist, arising as a consequence of alternate translational initiation. This species, now termed PKIβ-78, has been synthesized by bacterial expression, demonstrated to be equipotent with PKIβ-70, and also now demonstrated to occur in vivo. By Western blot analyses, six additional species of PKIβ are also evident in tissues. Two of these represent the phospho forms of PKIβ-78 and PKIβ-70. The other four represent phospho and dephospho forms of two higher molecular mass PKIβ species. These latter forms are currently termed PKIβ-X and PKIβ-Y, awaiting the full elucidation of their molecular identity. In adult rat testis and cerebellum, PKIβ-70, PKIβ-X, and PKIβ-Y constitute 39, 23, and 32% and 15, 29, and 54% of the total tissue levels, respectively. In adult rat testis, 35–42% of each of these three species is present as a monophospho form, whereas no phosphorylation of them is evident in cerebellum. PKIβ-78 is present at much lower levels in both rat testis and cerebellum (∼6 and 2% of the total, respectively) and almost entirely as a monophospho species. PKIβ-78, like PKIβ-70, is a high affinity and specific inhibitor of the cAMP-dependent protein kinase. PKIβ-Y and PKIβ-X, in contrast, also significantly inhibit the cGMP-dependent protein kinase.